Various types of fluid flow control valves are used in applications where the valve is subjected to corrosive acidic or caustic liquids, or where the purity of the liquids which flow through the valve must be maintained. Such valves are constructed of relatively inert materials, e.g., fluoropolymers or other polymeric materials, or the valve surfaces which come into contact with the flowing liquids, or which potentially can come into contact with the liquids, are coated with inert materials. Such flow control valves are commonly biased closed by a spring force and are opened by means of a solenoid actuator, or by pneumatic or hydraulic pressure, or the like. When valve closure springs are used, it can be important that the force required to be exerted by the spring to close the valve is minimized. By minimizing the required spring force, the spring imparts less stress to the valve structures, thereby increasing the length of valve life.
Fluid control valves sometimes include a diaphragm which is in contact with the fluid and which provides a barrier against escape of the fluid into the valve operating mechanism or into the atmosphere. In some designs, a backup diaphragm is provided which, in combination with the barrier diaphragm, provides a chamber to contain any fluid which may leak through the barrier diaphragm. Such chambers are sometimes provided with leak ports, so that, if the barrier diaphragm fails, the fluid which passes through the diaphragm into the chamber will be detected and appropriate action can be taken.
For example, U.S. Pat. No. 4,010,769 discloses a valve which incorporates a barrier diaphragm which contacts the fluid which flows through the valve. A second diaphragm is in the valve above the first diaphragm, and a leak port is between the diaphragms. Any fluid which may leak through the barrier diaphragm will be detected by means of the leak port and appropriate corrective action can be taken.
When a valve incorporates a diaphragm which contacts the fluid in a system, and the diaphragm is connected to the valve operating mechanism, as is the case with the valve disclosed in the '769 patent, any force which the fluid exerts on the diaphragm is transmitted to the valve operating mechanism and, thus, affects the operation of the valve. For example, in the '769 valve, a spring biases the valve closed and the valve opens by means of a solenoid. Any force exerted on the barrier diaphragm by the fluid in the system will tend to open the valve. Therefore, a larger spring is required to hold the valve closed than would be necessary if the valve was designed so that the force on the diaphragm tending to open the valve would be counterbalanced by another force in the opposite direction. The use of a larger spring results in more stresses than necessary being imparted on the valve structure, thereby tending to reduce the length of the life of the valve.
When a valve is provided with a diaphragm that is attached to the valve's operating mechanism which therefore moves with the mechanism as the valve opens and closes, the diaphragm can fail due to fatigue cracking. Usually, the greater the distance the diaphragm moves, and the more stretch and strain that is applied to the diaphragm during each cycle, the fewer cycles the diaphragm will be able to withstand before failing. Thus, it is important to minimize the length of diaphragm travel, and the strain on the diaphragm, to increase valve life.
U.S. Pat. No. 5,261,422 describes a diaphragm valve that is constructed to minimize spring force required to close the valve and, thereby reduce the stress on the valve components and increase valve life. Referring to FIG. 1, a three-way valve embodiment 10 disclosed in the '422 patent comprises a valve body 12 having a top 14 and a bottom 16, with a fluid inlet passage 18 through the side of the valve body 12 at a first location, a first fluid outlet passage 20 through the side of the valve body at a second location, and a second fluid outlet passage 22 through the side of the valve body at a third location. The first, second and third locations are spaced apart radially from each other around the body of the valve.
An upper valve seat 24 facing toward the valve body top 14 is located in the valve body between the inlet passage 18 and the first outlet passage 20. A lower valve seat 26 facing toward the valve body bottom 16 is located in the valve body between the inlet passage 18 and the second outlet passage 22. A cap 28 is removably mounted on the valve body top 14, and a first flexible imperforate diaphragm 30 is mounted on the inside of the cap. A second flexible imperforate diaphragm 32 is mounted across the upper portion of the valve body above the upper facing valve seat 24. The second diaphragm 32 is spaced below the first diaphragm 30 and forms an upper barrier for fluid flowing through the valve. The space between the first and second diaphragms forms an upper fluid containment chamber 34. A base 36 is removably mounted on the valve body bottom 16. A third flexible imperforate diaphragm 38 is mounted across a lower portion of the valve body 12 below the lower valve seat 26. The third diaphragm 38 forms a lower barrier for fluid flowing through the valve.
A poppet assembly 40 is connected between the second and third diaphragms and moves with the diaphragms. The poppet assembly 40 comprises a lower valve plug 42 connected to the upwardly facing surface of the third diaphragm 38, and an upper valve plug 44 connected to the downwardly facing surface of the second diaphragm 32. The lower valve plug 42 is configured to engage the lower facing valve seat 26 to stop the flow of fluids from the inlet 18 through the second outlet passage 22. The upper valve plug 44 is configured to engage the upper facing valve seat 24 to stop the flow of fluids from the inlet 18 through the first outlet passage 20.
A valve stem 46, which has one end integrally formed with one of the upper or lower valve plugs, extends through the center portion of the valve body 12, with the other end of the valve stem removably connected to the other valve plug. The connection between the valve stem and the valve plug forms a fluid-tight seal between the valve stem and the plug. A bolt 48 is disposed through the valve stem 46 and is used to attach the lower valve plug 42 thereto, and extends through the third diaphragm 38.
A spring 50 is in the space between the third diaphragm 38 and the base 36 for biasing the poppet assembly 40 and the connected second and third diaphragms in an upwardly direction for engaging the lower valve plug 42 with the downwardly facing lower valve seat 26 to stop the flow of fluids from the inlet 18 through the second outlet passage 22, while, at the same time, disengaging the upper valve plug 44 from the upwardly facing upper valve seat 24 to allow flow of fluids from the inlet 18 through the first outlet passage 20. Means are provided to counteract the spring force for moving the poppet assembly 40 and the connected second and third diaphragms in a downwardly direction for engaging the upper valve plug 44 with the upwardly facing valve seat 26 to stop the flow of fluids from the inlet 18 through the first outlet passage 20.
While the valve disclosed in the '422 patent is designed to use a minimum spring force for biasing the valve, and to reduce the distance the diaphragm must travel and the strain on the diaphragm so that the operation life of the valve is enhanced, there are design features of the valve that can be improved upon in an effort to: (1) further minimize the potential for contaminating chemically pure liquids by contact of leaking liquid with metallic valve elements; (2) provide an improved leak-tight seal between the respective valve plugs and valve seats; and (3) further minimize the number of potential leak paths through the valve. It is, therefore, desired to provide to the art an improved diaphragm valve for use with either chemically pure or corrosive liquids that comprises such improved design features.